1. Field of the Invention
The present invention relates to a controller and a control method of a permanent magnet type rotary motor.
Priority is claimed on Japanese Patent Application No. 2006-175220, filed Jun. 26, 2006, the contents of which are incorporated herein by reference.
2. Description of the Related Art
A conventional controller has been known for controlling voltage applied to an armature from a stator, which generates rotating magnetic field for rotating a rotator, to be less than a maximum voltage corresponding to source voltage by a vector control using a rotatory magnetic flux coordinate in which a field direction of a rotator having a permanent magnet is defined as a field axis and a direction perpendicular to the field axis is defined as a torque axis (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2002-95300).
In the controller, when a counter electromotive force increases depending on operating conditions of an electric motor and a voltage magnitude applied to the electric motor becomes more than the maximum voltage corresponding to the source voltage, a weak field control of controlling a current phase is performed by correcting a field-axis target current so as to equivalent weaken an intensity of magnetic field of the rotator.
However, in the conventional controller in a coordinate plane in which the torque axis is defined as a Y axis and a field axis is defined as an X axis, when the voltage magnitude exists in the first quadrant and the second quadrant, that is, when a voltage advance is less than 180°, the voltage magnitude can be converged into the inside of a maximum source voltage by a weak field control.
However, when the voltage magnitude exists in the third quadrant, that is, when the voltage advance is 180° or more, the voltage magnitude cannot be converged to be less than the maximum source voltage by the weak field control.
Specifically, in an electric motor for rotating a rotator by the use of a magnet torque between a rotating magnetic field generated by the armature and a permanent magnet of the rotator, and a rotating torque between the rotating magnetic field and a magnet core of the rotator, that is, a reluctance torque as shown in FIG. 5, the possible total torque is in maximum in an area in which a voltage advance is 180° or more. Accordingly, it is required that an electrification corresponding to a source voltage is properly controlled on the voltage magnitude in the third quadrant.
The present invention was made in view of the above-mentioned circumstances and has an object of providing a controller and a control method of a permanent magnet type rotary motor capable of performing an appropriate electrification control.